Indexing of zero-dimensional MArrays

[TheBB]

Zero-dimensional mutable arrays must implement an "empty" indexing method to work with some other functions, e.g. show:

julia> v = MArray{Tuple{},Int,0,1}(1)
0-dimensional MArray{Tuple{},Int64,0,1}:
Error showing value of type MArray{Tuple{},Int64,0,1}:
ERROR: ArgumentError: invalid index: () of type Tuple{}

This works for SArrays because they are specialized as "scalars", and this method is defined for them, but MArrays aren't.

[andyferris]

Good catch.